This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-186989, filed Jun. 30, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a temperature detector circuit for outputting digital data according to a temperature in atmosphere the detector circuit has been installed. In particular, the present invention relates to an improvement which allows restriction of an occurrence of an output error caused by dispersion in manufacture of an element for generating an analog signal according to an atmospheric temperature.
A number of semiconductor device systems are required to make adjustment according to a temperature in atmosphere in which the systems have been installed. For example, it is known that, in an oscillator circuit for generating a clock signal using a crystal oscillator, an oscillation frequency changes according to the atmospheric temperature. That is, in general, in the crystal oscillator, a specific oscillation frequency is determined depending on its cutting method and thickness, and however, the oscillation frequency varies depending on the temperature change of the atmosphere in which the oscillator has been installed. Frequency variation characteristics for the temperature of the crystal oscillator is expressed by a tertiary function.
In order to always oscillate an oscillator circuit using such crystal oscillator at a constant frequency without depending on the atmospheric temperature, it is required to generate a control signal according to the atmospheric temperature and control an operation of the oscillator circuit based on this control signal. A temperature detector circuit is used to generate a control signal according to the atmospheric temperature.
FIG. 1 is a block diagram showing an IC temperature detector circuit which has been conventionally used. In this circuit, a constant current is supplied to a diode 52 by means of a constant current circuit 51, and a forward drop voltage Vf obtained at an anode of the diode 52 is digital-converted by means of an AD converter 53, whereby a digital output according to the atmospheric temperature is obtained. That is, this temperature detector circuit is adopted to measure a temperature utilizing a temperature coefficient (in general, xe2x88x922 mV/xc2x0 C.) which the forward drop voltage Vf of the diode 52 has.
However, there has been a problem that dispersion in characteristics of the diode 52 occurs due to various fluctuation factors in an IC manufacturing process, whereby a difference occurs with a digital output from a different circuit under the same temperature condition.
In a conventional temperature detector circuit, a difference occurs with a digital output under the same temperature condition due to various fluctuation factors during a process for manufacturing an element for generating an analog signal according to the atmospheric temperature. As a result, there has been a problem that control properties and stability are lost in a system in which operation is controlled based on the digital output from this temperature detector circuit.
It is an object of the present invention to provide a temperature detector circuit capable of obtaining the substantially same digital output under the same temperature condition without depending on various fluctuation factors during a process for manufacturing an element for generating an analog signal according to the atmospheric temperature.
According to a first aspect of the present invention, there is provided a temperature detector circuit comprising: an analog signal generator circuit configured to generate an analog signal which changes according to the atmospheric temperature; an AD converter circuit configured to receive the analog signal and convert the analog signal into digital data to be output; a data storage circuit configured to store correction data in advance according digital data obtained by the AD converter circuit under a known arbitrary temperature condition and read the stored correction data; and a calculating circuit configured to receive digital data obtained by the AD converter circuit under an unknown temperature condition and the correction data read from the data storage circuit, and output digital data corrected by performing calculation between these data.
According to a second aspect of the present invention, there is provided an oscillator circuit comprising: an analog signal generator circuit configured to generate an analog signal which changes according to the atmospheric temperature; an AD converter circuit configured receive the analog signal and convert the analog signal into digital data to be output; a data storage circuit configured to store correction data in advance according to digital data obtained by the AD converter circuit under a known arbitrary temperature condition, and read the stored correction data; a calculating circuit configured to receive digital data obtained by the AD converter circuit under an unknown temperature condition and correction data read from the data storage circuit, and output the digital data corrected by performing calculation between these data; a DA converter circuit configured to receive the corrected digital data output from the calculating circuit and convert the digital data into an analog signal to be output; a crystal oscillator having one end and the other end; a feedback circuit connected between one end and the other end of the crystal oscillator; a first capacitor connected between one end of the crystal oscillator and a supply node of a determined voltage; a second capacitor connected between the other end of the crystal oscillator and the supply node of the predetermine voltage; and a variable capacitor element connected in series into the second capacitor between one end of the crystal oscillator and the supply node of the predetermined voltage, the element receiving the analog signal output from the DA converter circuit and causing a value to be changed according to the analog signal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.